The collection and reinfusion of a patient's own blood, referred to as autologous blood, offers a number of recognized benefits. For example, the use of autologous blood reduces concerns relating to the possibility of disease transmission via donor blood transfusions, referred to as homologous blood, as well as concerns regarding febrile/allergic reactions. Additionally, autologous blood recovery ensures the rapid availability of blood and reduces or eliminates the need for compatibility testing on such blood since the procedure is most typically completed in an operating room. Further, the use of autologous blood provides red blood cells which are generally superior in quality to banked blood and reduces any quantity of homologous blood otherwise needed. The use of autologous blood is also desirous to many patients for psychological and/or religious reasons.
Intraoperative procedures where autologous blood salvage is currently employed include cardiac and vascular surgery. Specialties which employ autologous blood salvage include orthopedics, plastic and reconstructive surgery, neurosurgery, solid organ transplants, general surgery, gynecology and trauma.
In a typical blood salvage procedure, blood is removed from or about a surgical site via a hand-held suction device, mixed with an anticoagulant, and transferred to a reservoir for subsequent transfer for batch processing. In connection with such collection/transfer of salvaged blood, the blood is typically filtered to remove debris and defoamed to remove entrained gaseous components (e.g. air) utilizing separate in-line filter devices and defoaming devices through which the salvaged blood is sequentially transferred. During batch processing, the salvaged blood and a wash solution are separately pumped in sequence through a centrifuge to separate red blood cells and achieve a degree of washing. Following processing, the red blood cells are removed from the centrifuge for reinfusion to the patient.
Another blood processing procedure is apheresis. Apheresis is a procedure of separating the blood into its various components via centrifugation. By appropriate adjustment of the separation instrument, a selected portion of the blood can be recovered while the rest of the blood is returned to the donor. Examples include plasmapheresis, plateletpheresis and red blood cell collection.
Plasma sequestration is a procedure which may include both plasmapheresis and plateletpheresis. Plasmapheresis is a process whereby plasma containing few cellular components (i.e., platelet poor plasma) is collected. Plateletpheresis is a process whereby plasma containing many cellular components (i.e., platelet rich plasma) is collected. This process also commonly uses centrifugation as its separation mechanism. The plasma component as well as the cellular components may be returned to the patient at the appropriate time.
In blood salvage and red cell collection procedures the objective is to obtain a high quality and amount of red blood cells in the least amount of overdue procedure time. A way to monitor the quality of the procedure is by measuring the hematocrit of the processed blood and maintaining it in a desired range. Methods of doing this include those disclosed in U.S. Pat. No. 5,385,539 (Maynard), which describes a hematocrit sensor used in a plasma separator apparatus. The hematocrit sensor continuously monitors the hematocrit level of processed blood, and adjusts the parameters of the plasma separator apparatus to compensate for a hematocrit that is too high or too low. However, many problems remain in this area, including, for example, variability in the measured hematocrit due to loss of hematocrit sampling data caused by non-blood substances such as air bubbles, or other obstructions in the blood flow path (e.g. clots, fat, etc.) that interfere with the detector signal. In addition, operator error remains a problem with such blood separation and measurement/analysis systems.